In a side airbag device described in the following Patent Literature 1, a side airbag is partitioned into a first inflating section (rear bag section) and a second inflating section (front bag section) by a partition wall (front-rear partition) disposed at a position corresponding to a rib region of an occupant in position. An inflator is provided inside the first inflating section, and gas generated from the inflator is supplied through communicating ports formed in the front-rear partition into the front bag section. With such a configuration, the rear bag section is set to have a higher pressure than that of the front bag section, thereby securing an initial restraint performance for an occupant in position, and also suppressing influence on the occupant even if the occupant is in an inappropriate position (out of position). Examples of the conventional technology relating to the present invention include the following Patent Literatures 2 to 6.